<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<style>
.header{ 
    margin:0 auto; 
    max-width: 960px; 
    height:100px; 
    background-color: blue; 
} 
.nav{ 
    margin: 0 auto; 
    max-width:800px; 
    background-color: darkgray; 
    height: 50px;
} 
.content{ 
    margin: 0 auto;
    max-width: 800px; 
    height: 400px;
    background-color: aquamarine; 
} 
.footer{ 
    margin: 0 auto; 
    max-width: 960px; 
    height:100px; 
    background-color: aqua; 
}

</style>

<script type="text/javascript">
    const a = 20;
    const b = 30;
    const string = `${a}+${b}=${a + b}`;
    console.log(string);

</script>

<body>
    <div class="header">
        <div class="nav"></div>
    </div>
    <div class="content"></div>
    <div class="footer"></div>
</body>
</html>

